1. Field of the Invention
The present invention generally relates to a liquid developing device. More specifically, the present invention relates to a liquid developing device that develops electrostatic latent images using liquid toner, and to a wet image forming device that includes the liquid developing device.
2. Background Information
Usually, image forming devices based on electrophotography, electrostatic latent images on a photosensitive drum are developed using powder toner. However, liquid developing devices in which electrostatic latent images are developed using liquid toner that is concentrated toner liquid diluted with carrier liquid have been proposed as seen in, for example, Japanese Patent Application Laid-open No. 2001-305867.
A liquid toner storage tank that stores liquid toner to be applied to the photosensitive drum is respectively supplied with concentrated toner liquid and carrier liquid from a toner liquid cartridge and a carrier cartridge. The concentrated toner liquid and carrier liquid are mixed and stored in the liquid toner storage tank. In order to obtain high quality images in an image forming device, it is necessary to maintain appropriately the toner solids content (toner powder as a percentage of the liquid toner) of the liquid toner in the liquid toner storage tank. Therefore the toner solids content of the liquid toner is constantly measured, and based on the measured value, the supplied quantity of concentrated toner liquid or carrier liquid is adjusted. The toner solids content is measured using for example an optical sensor.
In the developing device according to Japanese Patent Application Laid-open No. 2001-305867, the light emitting element and the light receiving element of the optical sensor are disposed mutually in opposition and positioned to sandwich the liquid toner. The toner solids content is measured based on, for example, the output current value of the light receiving element.
In this measurement method, an equation that expresses the relationship between the output value of the optical sensor and the toner solids content of the liquid toner is obtained in advance. The output value of the optical sensor obtained by measuring the liquid toner is entered into the equation that has been obtained in advance, to calculate the toner solids content of the liquid toner.
However, strictly speaking, the properties of the concentrated toner liquid in the toner liquid cartridges varies with each cartridge. Also, the properties of the carrier liquid in the carrier cartridges varies with each cartridge. Therefore, when these cartridges are changed, the electrical conductivity and the optical transmittance of the liquid toner varies. Therefore, in the conventional method that uses an equation, there is the possibility that the toner solids content of the liquid toner cannot be accurately measured. If the toner solids content cannot be accurately measured, the concentration of the liquid toner supplied to the photosensitive drum cannot be appropriately maintained, and it is not possible to obtain good images stably.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved liquid developing device and wet image forming device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.